# Patent

## Title
Piezoelectric material, piezoelectric element, multilayered piezoelectric element, manufacturing method for multilayered piezoelectric element, liquid discharge head, liquid discharge device, ultrasonic motor, optical device, vibration device, dust removing device, imaging device, and electronic device

## Abstract

Provided is a piezoelectric material that is free of lead and potassium, has satisfactory insulation property and piezoelectricity, and has a high Curie temperature. The piezoelectric material includes a perovskite-type metal oxide represented by the following general formula (1): General formula (1) (NaxM1-y)(Zrz(Nb1-wTaw)y(Ti1-vSnv)(1-y-z))O3 where M represents at least any one of Ba, Sr, and Ca, and relationships of 0.80≦x≦0.95, 0.85≦y≦0.95, 0<z≦0.03, 0≦v<0.2, 0≦w<0.2, and 0.05≦1−y−z≦0.15 are satisfied.

## Background
TECHNICAL FIELD
The present invention relates to a piezoelectric material, and more particularly, to a lead-free piezoelectric material. The present invention also relates to a piezoelectric element, a multilayered piezoelectric element, a manufacturing method for a multilayered piezoelectric element, a liquid discharge head, a liquid discharge device, an ultrasonic motor, an optical device, a vibration device, a dust removing device, an imaging device, and an electronic device, which use the piezoelectric material.
BACKGROUND ART
Lead zirconate titanate containing lead is a typical piezoelectric material, and is used in a variety of piezoelectric devices such as an actuator, an oscillator, a sensor, and a filter. However, it has been pointed out that, when a piezoelectric device containing lead is once scrapped and exposed to acid rain, the lead content in the piezoelectric material may be transferred into the soil to adversely affect the ecosystem. Accordingly, in order to exclude lead from piezoelectric devices, research and development on lead-free piezoelectric materials are actively conducted.
Currently, a typical lead-free piezoelectric material that has been widely researched is a piezoelectric material containing potassium niobate (KNbO3). However, when a piezoelectric material containing potassium is synthesized, it has been difficult to weigh raw material (for example, potassium carbonate) powder precisely at an intended molar ratio owing to hygroscopic property of the raw material powder. Further, the piezoelectric material containing potassium niobate (KNbO3) has deliquescence, and hence piezoelectricity of piezoelectric ceramics containing potassium niobate is sometimes degraded with the passage of time.
NPL 1 reports, as a piezoelectric material free of lead and potassium, a solid solution (hereinafter referred to as “NN—BT”) of sodium niobate (NaNbO3) and barium titanate (BaTiO3), which is an antiferroelectric. Non Patent Literature 1 discloses that a piezoelectric constant d33 of piezoelectric ceramics containing sodium niobate and barium titanate at a ratio of 9:1 is 147 pC/N.
PTL 1 provides a method of manufacturing a niobic acid-based piezoelectric porcelain having a high Curie temperature and satisfactory piezoelectric property. Patent Literature 1 discloses that a niobic acid-based piezoelectric porcelain that is a solid solution of NN—BT and strontium titanate (SrTiO3) has a piezoelectric constant d33 of 14 to 126 μm/V.
CITATION LIST
Patent Literature
PTL 1: Japanese Patent Application Laid-Open No. 2008-156172
Non Patent Literature
NPL 1: J. T. Zeng et al., “Journal of the American Ceramic Society,” 2006, Volume 89, pp. 2828-2832
SUMMARY OF INVENTION
Technical Problem
The conventional technology has a problem in that the piezoelectric performance of NN—BT is insufficient.
The present invention has been accomplished so as to solve the above-mentioned problem, and is directed to providing a piezoelectric material that is free of lead and potassium, has a larger relative dielectric constant and piezoelectric constant d33 than those of NN—BT, and has satisfactory insulation property. The present invention also provides a piezoelectric element using the piezoelectric material, a multilayered piezoelectric element, a manufacturing method for a multilayered piezoelectric element, a liquid discharge head, a liquid discharge device, an ultrasonic motor, an optical device, a vibration device, a dust removing device, an imaging device, and an electronic device.
Solution to Problem
In order to solve the above-mentioned problem, according to a first aspect of the present invention, there is provided a piezoelectric material, including a perovskite-type metal oxide represented by the following general formula (1):

(NaxM1-y)(Zrz(Nb1-wTaw)y(Ti1-vSnv)(1-y-z))O3  General formula (1)

(where M represents at least any one of Ba, Sr, and Ca, and relationships of 0.80≦x≦0.95, 0.85≦y≦0.95, 0<z≦0.03, 0≦v<0.2, 0≦w<0.2, and 0.05≦1−y−z≦0.15 are satisfied). According to a second aspect of the present invention, there is provided a piezoelectric element, including at least: a first electrode; a piezoelectric material; and a second electrode, in which the piezoelectric material includes the piezoelectric material of the present invention.

According to a third aspect of the present invention, there is provided a multilayered piezoelectric element, including a piezoelectric material layer and an electrode layer including an internal electrode, which are alternately stacked, in which the piezoelectric material includes the piezoelectric material of the present invention.
According to a fourth aspect of the present invention, there is provided a manufacturing method for the multilayered piezoelectric element, including at least: a step (A) of obtaining a slurry by dispersing a metal compound containing Na, Nb, Ti, and Zr; a step (B) of obtaining a compact from the slurry; a step (C) of forming an electrode on the compact; and a step (D) of obtaining a multilayered piezoelectric element by sintering a compact in which the compact containing the metal compound and the electrode are stacked alternately, the step (D) being performed at a sintering temperature of 1,200° C. or less.
According to a fifth aspect of the present invention, there is provided a liquid discharge head, including at least: a liquid chamber including a vibration unit including one of the above-mentioned piezoelectric element and the above-mentioned multilayered piezoelectric element; and a discharge port communicating with the liquid chamber.
According to a sixth aspect of the present invention, there is provided a liquid discharge device, including: a conveyance unit for a recording medium; and the above-mentioned liquid discharge head.
According to a seventh aspect of the present invention, there is provided an ultrasonic motor, including at least: a vibration body including one of the above-mentioned piezoelectric element and the above-mentioned multilayered piezoelectric element; and a moving body to be brought into contact with the vibration body.
According to an eighth aspect of the present invention, there is provided an optical device, including a drive unit including the above-mentioned ultrasonic motor.
According to a ninth aspect of the present invention, there is provided a vibration device, including a vibration body including one of the above-mentioned piezoelectric element and the above-mentioned multilayered piezoelectric element.
According to a tenth aspect of the present invention, there is provided a dust removing device, including a vibration unit including the above-mentioned vibration device.
According to an eleventh aspect of the present invention, there is provided an imaging device, including at least: the above-mentioned dust removing device; and an imaging element unit, in which a vibration member of the dust removing device and a light receiving plane side of the imaging element unit are sequentially disposed on the same axis.
According to a twelfth aspect of the present invention, there is provided an electronic device, including a piezoelectric acoustic component including one of the above-mentioned piezoelectric element and the above-mentioned multilayered piezoelectric element.
Advantageous Effects of Invention
According to the present invention, a piezoelectric material that is free of lead and potassium, has satisfactory insulation property and piezoelectricity, and has a high Curie temperature can be provided. The piezoelectric material of the present invention does not use lead, and thus has less impact on the environment. Further, the piezoelectric material of the present invention does not use potassium, and thus is excellent in sintering performance and in resistance to humidity.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic view illustrating a configuration of a piezoelectric element according to an embodiment of the present invention.
FIGS. 2A and 2B are schematic sectional views each illustrating a configuration of a multilayered piezoelectric element according to an embodiment of the present invention.
FIGS. 3A and 3B are schematic views each illustrating a configuration of a liquid discharge head according to an embodiment of the present invention.
FIG. 4 is a schematic view illustrating a liquid discharge device according to an embodiment of the present invention.
FIG. 5 is a schematic view illustrating the liquid discharge device according to the embodiment of the present invention.
FIGS. 6A and 6B are schematic views each illustrating a configuration of an ultrasonic motor according to an embodiment of the present invention.
FIGS. 7A and 7B are schematic views each illustrating an optical device according to an embodiment of the present invention.
FIG. 8 is a schematic view illustrating the optical device according to the embodiment of the present invention.
FIGS. 9A and 9B are schematic views each illustrating the case where a dust removing device is used as a vibration device according to an embodiment of the present invention.
FIGS. 10A, 10B and 10C are schematic views each illustrating a configuration of a piezoelectric element in the dust removing device of the present invention.
FIGS. 11A and 11B are schematic views each illustrating the principle of vibration of the dust removing device of the present invention.
FIG. 12 is a schematic view illustrating an imaging device according to an embodiment of the present invention.
FIG. 13 is a schematic view illustrating the imaging device according to the embodiment of the present invention.
FIG. 14 is a schematic view illustrating an electronic device according to an embodiment of the present invention.
FIG. 15 shows polarization-electric field hysteresis loops of sintered bodies of Comparative Example 5 and Examples 10 and 12 to 14 of the present invention.



DESCRIPTION OF EMBODIMENTS
Embodiments for carrying out the present invention are described in the following.
The present invention provides a lead-free piezoelectric material that is based on NN—BT and has satisfactory piezoelectricity and insulation property. Note that the piezoelectric material of the present invention may be used in various applications such as a capacitor, a memory, and a sensor, utilizing its property as a dielectric.
A piezoelectric material of the present invention includes a perovskite-type metal oxide represented by the following general formula (1):

(NaxM1-y)(Zrz(Nb1-wTaw)y(Ti1-vSnv)(1-y-z))O3  General formula (1)

(where M represents at least any one of Ba, Sr, and Ca, and relationships of 0.80≦x≦0.95, 0.85≦y≦0.95, 0<z≦0.03, 0≦v<0.2, 0≦w<0.2, and 0.05≦1−y−z≦0.15 are satisfied). In the present invention, the perovskite-type metal oxide refers to a metal oxide having a perovskite-type structure (sometimes referred to as “perovskite structure”) that is ideally a cubic structure as described in Iwanami Rikagaku Jiten 5th Edition (published by Iwanami Shoten on Feb. 20, 1998). A metal oxide having a perovskite structure is generally represented by a chemical formula: ABO3. In the perovskite-type metal oxide, elements A and B occupy specific positions in a unit cell, which are called an A site and a B site, respectively, in the form of ions. For example, in the case of a cubic unit cell, the A site element occupies the corners of a cubic, and the B site element occupies a body-centered position of the cubic. An oxygen (O) element occupies the face-centered positions of the cubic as an anion.

The metal oxide represented by the general formula (1) means that metal elements positioned at the A site are Na and M (at least any one of Ba, Sr, and Ca), and metal elements positioned at the B site are Zr, Nb, Ta, Ti, and Sn. Note that part of Na and M may be positioned at the B site. Similarly, part of Ti and Zr, Nb, and Ta and Sn may be positioned at the A site.
In the general formula (1), the molar ratio between the elements at the B site and the oxygen element is 1:3, and the case where the ratio of element amounts is slightly shifted (for example, 1.00:2.94 to 1.00:3.06) also falls within the scope of the present invention as long as the metal oxide has a perovskite-type structure as a primary phase. It can be determined through, for example, structure analysis by X-ray diffraction and electron beam diffraction that the metal oxide has a perovskite-type structure.
The form of the piezoelectric material according to the present invention is not limited and may be any one of ceramics, powder, a monocrystal, a film, a slurry, and the like. In particular, it is preferred that the piezoelectric material be ceramics. The term “ceramics” as used herein refers to an aggregate (also referred to as “bulk body”) of crystal grains, a so-called polycrystal, which contains a metal oxide as a basic component and is baked by a heat treatment. The ceramics include ones processed after sintering.
In the general formula (1), when x, which represents the abundance of Na at the A site, represents less than 0.8, Na becomes deficient with respect to the sum of Ta and Nb. Therefore, an impurity phase (phase having an X-ray diffraction pattern similar to that of Ba4Nb2O9, Ba6Ti7Nb9O42, Ba3Nb4Ti4O21, Ba3Nb3.2Ti5O21, or the like) is generated. The resistivity of a metal oxide sample containing an impurity phase in a great amount is as low as 107 to 108 Ωcm, and hence it is difficult to polarize such metal oxide sample.
Further, when x represents more than 0.95, the piezoelectricity is degraded. When x falls within a range of 0.80≦x≦0.95, the generation of an impurity phase can be suppressed and the piezoelectricity becomes satisfactory.
In the general formula (1), when y, which represents the total amount of Nb and Ta at the B site, represents less than 0.85, the Curie temperature becomes lower than 140° C. On the other hand, when y represents more than 0.95, the piezoelectricity is degraded. Accordingly, when y falls within a range of 0.85≦y≦0.95, the Curie temperature becomes 140° C. or more, and the piezoelectricity becomes satisfactory.
y more preferably falls within a range of 0.85≦y≦0.90 because the Curie temperature falls within a range of approximately 90° C. to 230° C., and the polarization treatment can be easily performed. y still more preferably falls within a range of 0.88≦y≦0.90 because the Curie temperature falls within a range of approximately 150° C. to 230° C., the polarization treatment can be easily performed, and there is a low risk that the piezoelectric performance is degraded owing to the heat during a device manufacturing step.
The term “Curie temperature” herein employed refers to a temperature at or above which the piezoelectricity of the piezoelectric material is lost. Herein, the temperature at which the dielectric constant becomes a local maximum in the vicinity of a phase transition temperature between a ferroelectric phase and a paraelectric phase is defined as the Curie temperature. Further, the perovskite-type metal oxide of the present invention has a successive phase transition temperature, at which successive phase transition from a tetragonal ferroelectric phase to an orthorhombic ferroelectric phase occurs, in a temperature region lower than the Curie temperature. At the successive phase transition temperature, the relative dielectric constant shows a local maximum or an inflection point, and hence the successive phase transition temperature can also be determined by evaluating the temperature dependence of the relative dielectric constant similarly to the Curie temperature. For example, a solid solution represented by 0.9NaNbO3-0.1BaTiO3 undergoes phase transition from an orthorhombic phase to a tetragonal phase to a cubic phase with an increase in temperature.
In the vicinity of the successive phase transition temperature, the piezoelectric performance becomes a local maximum. Therefore, in the case where predetermined piezoelectric performance not depending on temperature is required in a driving temperature range (for example, −30° C. to 60° C.) of a device, it is desired that the successive phase transition be absent in the driving temperature range. On the other hand, in the case where an increase in piezoelectric performance at a specific temperature is prioritized compared to the case where the piezoelectric performance does not depend on temperature in a driving temperature range of a device, the successive phase transition can be set in the driving temperature range of a device. The material whose successive phase transition temperature can be adjusted in accordance with the specification of a device is excellent because of high general versatility.
In the piezoelectric material of the present invention, the dielectric constant at room temperature increases, and the piezoelectric performance is enhanced, because 3 mol % or less of the B site are replaced by Zr with respect to NN—BT. In the general formula (1), z, which represents the abundance of Zr at the B site, represents more than 0.03, the resistivity decreases, and further the sintering temperature required for obtaining a sample having a relative density of 95% or more increases by 50° C. or more. The relative density refers to a ratio of an actually measured density with respect to a theoretical density. The theoretical density can be calculated from a molecular weight and a lattice constant of a material. The actually measured density can be measured, for example, by the Archimedes method.
Further, the replacement of 3 mol % or less of the B site by Zr with respect to NN—BT enhances the insulation resistance of the piezoelectric material of the present invention. When z represents more than 0.03, the resistivity of a material rather decreases.
In the piezoelectric material of the present invention, less than 20 mol % of the Ti site of NN—BT may be replaced by Sn. When v, which represents the replacement amount of Sn with respect to the Ti site, is changed in a range of 0<v<0.2, the Curie temperature and the successive phase transition temperature of the piezoelectric material of the present invention can be adjusted in accordance with the practical use. For example, by adjusting the Curie temperature, the temperature for the polarization treatment can be decreased. Further, by adjusting the successive phase transition temperature, the piezoelectricity at a specific temperature can be rendered a local maximum or a change in piezoelectricity with respect to temperature can be decreased. However, when the Ti replacement amount v by Sn becomes 0.2 or more, the Curie temperature decreases by 60° C. or more compared with the case where the piezoelectric material is free of Sn, and there is a high risk that the piezoelectric performance may be degraded owing to the heat given during the device manufacturing step. Further, when the piezoelectric material is free of Sn, the temperature range in which the piezoelectric material of the present invention is tetragonal is enlarged. Accordingly, as long as the polarization treatment can be performed easily, and it is not necessary to change the successive phase transition temperature with the amount of Sn, it is preferred that a relationship of v=0 be satisfied.
In the piezoelectric material of the present invention, less than 20 mol % of the Nb site of NN—BT may be replaced by Ta. When w, which represents the replacement amount of Ta with respect to the Nb site, is changed in a range of 0<w<0.2, the Curie temperature and the successive phase transition temperature of the piezoelectric material of the present invention can be adjusted in accordance with the practical use. By adjusting the Curie temperature, the temperature for the polarization treatment can be decreased. By adjusting the successive phase transition temperature, the piezoelectricity at a specific temperature can be rendered a local maximum or a change in piezoelectricity with respect to temperature can be decreased. However, when the Nb replacement amount w by Ta becomes 0.2 or more, the Curie temperature decreases to room temperature. As a result, there is a remarkably high risk that the piezoelectric performance may be degraded owing to the heat given during the device manufacturing step. Further, in the case where the piezoelectric material of the present invention is sintered at a temperature of 1,200° C. or less, it is difficult that the NN—BT phase and the NaTaO3 phase form a solid solution, and a NaNbO3 phase is generated as a second phase. On the other hand, when the piezoelectric material of the present invention is free of Ta, the sintering temperature of the piezoelectric material of the present invention can be decreased to the largest extent. Accordingly, as long as the polarization treatment can be performed easily and it is not necessary to change the successive phase transition temperature with the amount of Ta, it is preferred that a relationship of w=0 be satisfied.
In the general formula (1), when (1−y−z), which represents the total amount of Ti and Sn at the B site, represents less than 0.05, the piezoelectricity is degraded. On the other hand, when (1−y−z) represents more than 0.15, the Curie temperature becomes less than 140° C.
The piezoelectric material of the present invention more preferably includes a perovskite-type metal oxide represented by the following general formula (2):

(NaxBa1-y-a-bCaaSrb)(ZrzNbyTi1-y-z)O3  General formula (2)

(where relationships of 0.80≦x≦0.95, 0.85≦y≦0.95, 0<z≦0.03, 0.05≦1−y−z≦0.15, 0≦a≦0.1, 0≦b≦0.1, and 0≦a+b≦0.15 are satisfied).

In the general formula (2), when a, which represents the abundance of Ca at the A site, or b, which represents the abundance of Sr at the A site, represents more than 0.1, there is a risk in that the Curie temperature and successive phase transition temperature may decrease by 10° C. or more compared with those of a sample in which a relationship of a=b=0 is satisfied. Accordingly, as long as it is not necessary to adjust the successive phase transition temperature, it is preferred that a and b each represent 0.1 or less, and it is more preferred that a relationship of a=b=0 be satisfied.
It is preferred that the piezoelectric material of the present invention contain 2 mol % or less (excluding 0 mol %) of Cu with respect to 1 mol of the perovskite-type metal oxide. When the piezoelectric material of the present invention contains 2 mol % or less of Cu, the resistivity, electromechanical coupling coefficient, electromechanical quality factor, Young's modulus, and density can be increased. Further, the sintering temperature of the piezoelectric material of the present invention can be decreased. The sintering temperature refers to the minimum sintering temperature required for obtaining a sintered body having a relative density of 95% or more. Further, in the case where the spontaneous polarization of the piezoelectric material of the present invention is pinned, Cu can reduce the pinning of the spontaneous polarization. When the pinning is reduced, a remanent polarization value increases or a coercive field decreases in a polarization-electric field hysteresis loop. Further, it becomes easy to align the orientation of the spontaneous polarization by the polarization treatment. As a result, a phase difference of impedance between the resonance and the non-resonance increases and the electromechanical coupling coefficient increases.
Cu may be present at the A site (12-coordination), the B site (6-coordination), or at both the sites of the perovskite structure, or at the grain boundary of ceramics.
When a crystal containing sodium niobate as a component is sintered, Na evaporates or diffuses, and a sample composition after the sintering in which Na becomes insufficient with respect to Nb may be obtained. That is, defects occur at the A site. However, when an excess Na raw material is weighed at the time of weighing raw material powder, the insulation property of the sintered body is sometimes decreased. Accordingly, it is preferred that part of added Cu occupy the A site to compensate for defects. In some cases, it is preferred that raw materials be weighed so that Na becomes insufficient in a range not exceeding 5% with respect to Nb in the composition after the sintering and Cu be added.
When Cu occupies the A site to reduce the crystal defect, at least one of the following effects may be expected:
(1) an increase in resistivity;
(2) an increase in phase angle of impedance at the time of resonance frequency of the polarized piezoelectric material;
(3) an increase in remanent polarization value evaluated by polarization-electric field hysteresis loop measurement;
(4) an increase in electromechanical coupling coefficient;
(5) a decrease in mechanical quality factor;
(6) a decrease in Young's modulus; and
(7) a decrease in dielectric loss tangent (tan δ).
Further, when Cu occupies the B site, a defective dipole is formed together with oxygen defects to form an internal electric field. Accordingly, part of added Cu may occupy the B site.
When Cu occupies the B site, at least one of the following effects may be expected:
(1) a reduction in electromechanical coupling coefficient or piezoelectric constant;
(2) an increase in mechanical quality factor;
(3) an increase in Young's modulus; and
(4) generation of an internal electric field.
The magnitude of the internal electric field becomes a half of a difference in magnitude of positive and negative coercive fields obtained by the polarization-electric field hysteresis loop measurement. The direction of the defective polarization is also aligned with the direction of an applied electric field owing to the polarization treatment, and hence a sample subjected to the polarization can be used for estimating the intensity of an internal electric field. In the case where Cu is contained in both the A site and the B site, the above-mentioned effects appear in a superimposed manner. The superimposed effect of the addition can be controlled by the addition amount of Cu, and hence Cu may be contained in both the A site and the B site.
When Cu occupies the A site, the volume of the unit cell is decreased because Cu ions are smaller than Na ions and Ba ions.
When Cu occupies the B site, the volume of the unit cell is increased because Cu ions are larger than Nb ions and Ti ions. The volume of the unit call may be evaluated by X-ray diffraction.
For example, when Cu first occupies the A site and then occupies the B site, the volume of the unit cell is once decreased and then increased.
Further, Cu is not required to be present at any one of the A and B sites and may be present at the grain boundary. Cu accelerates liquid phase sintering owing to its low melting point. As a result, Cu is sometimes segregated at the grain boundary. When the liquid phase sintering is accelerated, pores in a sintered body decrease and the density of the sintered body increases. Further, as a result of the reduction of the pores, the mechanical quality factor increases and the Young's modulus increases. The distribution of Cu in a sample and an occupying site in a crystal can be evaluated even by an electron microscope, energy dispersive X-ray spectroscopy (EDX), X-ray diffraction, Raman scattering, or a transmission-type electron microscope.
When Cu is contained in an amount of more than 2 mol % with respect to 1 mol of the perovskite-type metal oxide, there is a risk in that an impurity phase is generated to decrease piezoelectricity.
It is preferred that the piezoelectric material of the present invention satisfy a relationship of x<y in the general formula (1). It is not preferred that M be rendered deficient with respect to the sum of Ti, Sn, and Zr even at the same A site, because abnormal grain growth is accelerated. Further, even when Cu occupies the M site, the valence numbers of both are equal, and hence the above-mentioned effects may not be obtained. When x is less than y, Cu is taken in a crystal lattice as a donor and the effect of the present invention is exhibited easily, and hence it is preferred that x be less than y. Further, it is preferred to adjust the composition of starting raw materials so that x becomes less than y. When x is equal to or more than y, the insulation property of a sample is degraded remarkably.
20% or less of Nb contained in the piezoelectric material of the present invention may be replaced by V. When part of Nb is replaced by V, the sintering temperature of the piezoelectric material can be decreased. 0 mol % or more to 5 mol % or less (excluding 0 mol %) of Ni may be added to 1 mol of the piezoelectric material of the present invention. When Ni is added, the piezoelectric constant and resistivity of the piezoelectric material can be increased, and the sintering temperature thereof can be decreased. 15% or less of Na contained in the piezoelectric material of the present invention may be replaced by Li. When part of Na is replaced by Li, the Curie temperature of the piezoelectric material can be increased.
In the case of forming the piezoelectric material of the present invention into a sintered body, a compact before being sintered needs to be formed. The compact refers to a solid substance formed from raw material powder. It is preferred that raw material powder has higher purity. The mixing of Mg greatly influences the piezoelectric performance of a sample, and hence it is preferred to use a raw material in which the content of Mg is small, in particular. As a forming method, there may be given uniaxial pressing, cold isostatic pressing, hot isostatic pressing, slip coating, and extrusion molding. When a compact is produced, it is preferred to use granulated powder. When the compact using the granulated powder is sintered, there is an advantage in that the size distribution of crystal grains of the sintered body is likely to be uniform.
No particular limitation is imposed on a method of granulating raw material powder of a piezoelectric material, and a spray drying method is the most preferred granulation method from such a viewpoint that the grain size of the granulated powder can be made more uniform.
Examples of the binder that may be used for granulation include polyvinyl alcohol (PVA), polyvinyl butyral (PVB), and an acrylic resin. The amount of the binder to be added is, with respect to the raw material power of the piezoelectric material, preferably 1 part by weight to 10 parts by weight, more preferably 2 parts by weight to 5 parts by weight from the viewpoint of increasing the density of a compact.
No particular limitation is imposed on a method of sintering the compact.
Examples of the sintering method include sintering using an electric furnace, sintering using a gas furnace, a conduction heating method, a microwave sintering method, a millimeter-wave sintering method, and hot isostatic pressing (HIP). The electric furnace and gas furnace for the sintering may be a continuous furnace or a batch furnace.
Although no particular limitation is imposed on a sintering temperature in the sintering method, it is preferred that the temperature be a temperature at which the respective compounds react with each other and the crystal sufficiently grows. The sintering temperature is preferably 1,050° C. or more to 1,300° C. or less, more preferably 1,100° C. or more to 1,200° C. or less from the viewpoint of setting the grain size in a range of 1 μm to 10 μm. A piezoelectric material sintered in the above-mentioned temperature range exhibits satisfactory piezoelectric performance. In order to stabilize the properties of a piezoelectric material obtained by the sintering treatment with good reproducibility, it is appropriate that the sintering treatment is performed for 2 hours or more to 48 hours or less with the sintering temperature being set constant in the above-mentioned range. Further, a sintering method such as a two-stage sintering method may be used, and a method in which temperature does not change suddenly is preferred in consideration of the productivity.
It is preferred that the piezoelectric material obtained by the sintering treatment be subjected to a heat treatment at a temperature equal to or higher than the Curie temperature after being polished. When the piezoelectric material is mechanically polished, a residual stress is generated inside the piezoelectric material. However, when the piezoelectric material is subjected to a heat treatment at the Curie temperature or more, the residual stress is relieved, and the piezoelectric property of the piezoelectric material becomes more satisfactory. Although the heat treatment time is not particularly limited, 1 hour or more is preferred.
When the crystal grain size of the piezoelectric material of the present invention is more than 100 μm, the strength may be poor in cutting and polishing. Further, when the crystal grain size is less than 0.3 μm, the piezoelectricity is degraded. Therefore, a preferred average grain size falls within a range of 0.3 μm or more to 100 μm or less.
When the piezoelectric material of the present invention is used as a film formed on a substrate, it is desired that the thickness of the piezoelectric material be 200 nm or more to 10 μm or less, more preferably 300 nm or more to 3 μm or less. This is because, when the film thickness of the piezoelectric material is 200 nm or more to 10 μm or less, a sufficient electromechanical converting function as a piezoelectric element may be obtained.
The method of laminating the above-mentioned film is not particularly limited. For example, there are given chemical solution deposition (CSD), a sol-gel process, metalorganic chemical vapor deposition (MOCVD), sputtering, pulse laser deposition (PLD), hydrothermal synthesis, and aerosol deposition (AD). Of those, chemical solution deposition or sputtering is the most preferred laminating method. By chemical solution deposition or sputtering, the area of a film formed may be increased with ease. It is preferred that the substrate used for the piezoelectric material of the present invention be a monocrystalline substrate cut and polished along a (001) plane or a (110) plane. With the use of a monocrystalline substrate cut and polished along a specific crystal plane, a piezoelectric material film formed on the surface of the substrate may also be strongly oriented in the same direction.
A piezoelectric element using the piezoelectric material of the present invention is described below.
FIG. 1 is a schematic view illustrating a configuration of a piezoelectric element according to an embodiment of the present invention. The piezoelectric element according to the present invention is a piezoelectric element including at least a first electrode 1, a piezoelectric material 2, and a second electrode 3, in which the piezoelectric material 2 is the piezoelectric material of the present invention.
The piezoelectric property of the piezoelectric material according to the present invention can be evaluated by forming the piezoelectric element including at least the first electrode and the second electrode. The first electrode and the second electrode are each formed of a conductive layer having a thickness of about 5 nm to 10 μm. A material therefor is not particularly limited and has only to be one to be generally used for a piezoelectric element. Examples thereof may include metals such as Ti, Pt, Ta, Ir, Sr, In, Sn, Au, Al, Fe, Cr, Ni, Pd, Ag, and Cu, and compounds thereof.
Each of the first electrode and the second electrode may be formed of one kind of those materials, or may be obtained by stacking two or more kinds thereof. The first electrode and the second electrode may be formed of different materials, respectively.
A manufacturing method for the first electrode and the second electrode is not limited. The first electrode and the second electrode may be formed by baking a metal paste or by sputtering, vapor deposition, or the like. In addition, both the first electrode and the second electrode may be patterned in desired shapes for use.
It is more preferred that the piezoelectric element have spontaneous polarization axes aligned in a certain direction. When the spontaneous polarization axes are aligned in a certain direction, the piezoelectric constant of the piezoelectric element increases.
A polarization method for the piezoelectric element is not particularly limited. The polarization treatment may be performed in the air or may be performed in an oil. A temperature at which the polarization is performed is preferably a temperature of 60° C. to 160° C. However, an optimum condition slightly varies depending on the composition of a piezoelectric material constituting the element. An electric field to be applied for performing the polarization treatment is preferably equal to or higher than the coercive field of the material, and is specifically 1 to 5 kV/mm.
The piezoelectric constant and electromechanical quality factor of the piezoelectric element may be determined by calculation, from the measurement results of a resonance frequency and an antiresonance frequency, which are obtained with a commercially available impedance analyzer, based on the standard of Japan Electronics and Information Technology Industries Association (JEITA EM-4501). This method is hereinafter referred to as resonance-antiresonance method.
Next, a multilayered piezoelectric element using the piezoelectric material of the present invention is described.
The multilayered piezoelectric element according to the present invention is a multilayered piezoelectric element including piezoelectric material layers and electrodes including an internal electrode stacked alternately, in which the piezoelectric material layers are formed of the piezoelectric material of the present invention.
FIGS. 2A and 2B are each a schematic sectional view illustrating a configuration of a multilayered piezoelectric element according to an embodiment of the present invention. The multilayered piezoelectric element according to the present invention is a multilayered piezoelectric element including piezoelectric material layers 54 and electrode layers including an internal electrode 55, the piezoelectric material layers and the electrode layers being stacked alternately, in which the piezoelectric material layers 54 are formed of the above-mentioned piezoelectric material. The electrodes may include external electrodes such as a first electrode 51 and a second electrode 53 in addition to the internal electrode 55.
FIG. 2A illustrates the configuration of the multilayered piezoelectric element of the present invention in which the piezoelectric material layers 54 of two layers and the internal electrode 55 of one layer are stacked alternately, and the multilayered structure is sandwiched between the first electrode 51 and the second electrode 53. However, as illustrated in FIG. 2B, the number of piezoelectric material layers and internal electrodes may be increased, and the number of the layers is not limited. The multilayered piezoelectric element of FIG. 2B has such a configuration that piezoelectric material layers 504 of nine layers and internal electrodes 505 (505a and 505b) of eight layers are stacked alternately, and the multilayered structure is sandwiched between a first electrode 501 and a second electrode 503, and has an external electrode 506a and an external electrode 506b for short-circuiting the alternately formed internal electrodes.
The internal electrodes 55, 505 and the external electrodes 506a, 506b do not need to be identical in size and shape to the piezoelectric material layers 54, 504, and may be divided into multiple portions.
The internal electrodes 55, 505 and the external electrodes 506a, 506b are formed of a conductive layer having a thickness of about 5 nm to 10 μm. A material therefor is not particularly limited and has only to be one to be generally used for a piezoelectric element. Examples thereof may include metals such as Ti, Pt, Ta, Ir, Sr, In, Sn, Au, Al, Fe, Cr, Ni, Pd, Ag, and Cu and compounds thereof. The internal electrodes 55, 505, the external electrodes 506a, 506b, the first electrode 51, 501, and the second electrode 53, 503 may be formed of one kind thereof, may be formed of a mixture or alloy of two or more kinds thereof, or may be formed of a multilayered body of two or more kinds thereof. Further, multiple electrodes may be respectively formed of materials different from each other. From the viewpoint that an electrode material is inexpensive, it is preferred that the internal electrodes 55, 505 contain at least any one kind of Ni and Cu. When at least any one kind of Ni and Cu is used for the internal electrodes 55, 505, the multilayered piezoelectric element of the present invention is preferably sintered in a reducing atmosphere.
In the multilayered piezoelectric element of the present invention, the internal electrode contains Ag and Pd, and a weight ratio M1/M2 between the content weight M1 of Ag and the content weight M2 of Pd is preferably 1.5≦M1/M2≦9.0, more preferably 2.3≦M1/M2≦4.0. A case where the weight ratio M1/M2 is less than 1.5 is not desired because the sintering temperature of the internal electrode increases. On the other hand, a case where the weight ratio M1/M2 is more than 9.0 is not desired because the internal electrode becomes island-shaped, resulting in in-plane non-uniformity.
As illustrated in FIG. 2B, multiple electrodes including the internal electrodes 505 may be short-circuited to each other for the purpose of making the phase of a driving voltage uniform. For example, the internal electrode 505a and the first electrode 501 may be short-circuited by the external electrode 506a. The internal electrode 505b and the second electrode 503 may be short-circuited by the external electrode 506b. The internal electrode 505a and the internal electrode 505b may be disposed alternately. Further, a mode in which the electrodes are short-circuited to each other is not limited. An electrode or wiring for short-circuit may be provided on a side surface of the multilayered piezoelectric element. Alternatively, the electrodes may be short-circuited to each other by providing a through-hole passing through the piezoelectric material layers 504 and providing a conductive material inside the through hole.
Next, a manufacturing method for the multilayered piezoelectric element using the piezoelectric material of the present invention is described.
A manufacturing method for a multilayered piezoelectric element according to the present invention includes at least: a step (A) of dispersing metal compound powder containing at least Na, Nb, Ti, and Zr to prepare a slurry; a step (B) of obtaining a compact from the slurry; a step (C) of forming an electrode on the compact; and a step (D) of sintering a compact in which the compact containing the metal compound powder and the electrode are stacked alternately to yield a multilayered piezoelectric element, the step (D) being performed at a sintering temperature of 1,200° C. or less. The metal oxide powder may contain copper. The powder as used herein is intended to mean an aggregate of solid particles. The aggregate may be an aggregate of particles containing Ba, Sr, Ca, Na, Ti, Zr, and Nb simultaneously, or may be an aggregate of multiple kinds of particles containing any element.
Examples of the metal compound powder in the step (A) may include powders of a Ba compound, a Sr compound, a Ca compound, a Na compound, a Ti compound, a Zr compound, a Nb compound, a Sn compound, a Ta compound, and a Cu compound.
Examples of the Na compound that may be used include sodium carbonate, sodium niobate, and sodium tantalate.
Examples of the Ba, Ca, and Sr compounds that may be used include oxides, carbonates, oxalates, acetates, nitrates, titanates, zirconates, zirconate titanates, and stannates of the respective elements.
Examples of the Ti compound that may be used include titanium oxide, barium titanate, barium zirconate titanate, and calcium titanate.
Examples of the Zr compound that may be used include zirconium oxide, barium zirconate, barium zirconate titanate, and calcium zirconate.
Examples of the Sn compound that may be used include tin oxide, barium stannate, barium stannate titanate, and calcium stannate.
When each of those Ti, Zr, and Sn compounds contains an alkaline earth metal such as Ba or Ca, a commercially available high-purity (e.g., purity of 99.99% or more) compound is preferably used.
Examples of the Nb compound that may be used include niobium oxide and sodium niobate.
Examples of the Ta compound that may be used include tantalum oxide and sodium tantalate.
Examples of the Cu compound that may be used include copper (I) oxide, copper (II) oxide, copper carbonate, copper (II) acetate, and copper oxalate.
A preparation method for the slurry in the step (A) is exemplified. A solvent is added in a weight of 1.6 to 1.7-fold with respect to the metal compound powder, followed by mixing. As the solvent, for example, toluene, ethanol, a mixed solvent of toluene and ethanol, n-butyl acetate, or water may be used. The components are mixed in a ball mill for 24 hours. After that, a binder and a plasticizer are added. Examples of the binder include polyvinyl alcohol (PVA), polyvinyl butyral (PVB), and an acrylic resin. When PVB is used as the binder, the solvent and PVB are weighed so that a weight ratio therebetween is, for example, 88:12. Examples of the plasticizer include dioctyl sebacate, dioctyl phthalate, and dibutyl phthalate. When dibutyl phthalate is used as the plasticizer, equal weights of dibutyl phthalate and the binder are weighed. Then, the mixing in a ball mill is performed again overnight. The amounts of the solvent and the binder are adjusted so that the viscosity of the slurry is 300 to 500 mPa·s.
The compact in the step (B) is a sheet-shaped mixture of the metal compound powder, the binder, and the plasticizer. As a method of obtaining the compact in the step (B), for example, there is given sheet forming. For example, a doctor blade method may be employed for the sheet forming. The doctor blade method is a method of forming a sheet-shaped compact involving applying the slurry onto the base material with a doctor blade and drying the applied slurry. As the base material, for example, a PET film may be used. It is desired that the surface of the PET film onto which the slurry is applied be coated with fluorine because the coating facilitates the peeling of the compact. The drying may be natural drying or hot-air drying. The thickness of the compact is not particularly limited and may be adjusted depending on the thickness of the multilayered piezoelectric element. The thickness of the compact may be increased by, for example, increasing the viscosity of the slurry.
Manufacturing methods for the electrodes, that is, the internal electrodes 505a, 505b and the external electrodes 506a, 506b in the step (C) are not limited. The electrodes may be formed by baking a metal paste, or may be formed by, for example, sputtering, vapor deposition, or a printing method. For the purpose of reducing a driving voltage, the thickness and pitch interval of the piezoelectric material layers 504 are reduced in some cases. In that case, there is selected a process involving forming a multilayered body including a precursor for the piezoelectric material layers 504 and the internal electrodes 505a, 505b and then sintering the multilayered body simultaneously. In that case, there is demanded an internal electrode material that does not undergo deformation and conductivity degradation at a temperature required for sintering the piezoelectric material layers 504. An inexpensive metal having a low melting point as compared to Pt, such as Ag, Pd, Au, Cu, or Ni, or an alloy thereof may be used for the internal electrodes 505 and the external electrodes 506a, 506b. In this connection, the external electrodes 506a, 506b may be formed after the sintering of the multilayered body. In that case, Al or a carbon-based electrode material may be used in addition to Ag, Pd, Cu, or Ni.
A method of forming the electrode is desirably a screen printing method. The screen printing method is a method involving providing a screen printing plate on a compact provided on a base material and applying a metal paste with a spatula from above the screen printing plate. A screen mesh is formed on at least part of the screen printing plate. Thus, the metal paste at a portion on which the screen mesh is formed is applied onto the compact. The screen mesh in the screen printing plate desirably has a pattern formed therein. An electrode can be patterned onto the compact by transferring the pattern onto the compact through use of the metal paste.
The electrode is formed in the step (C) and then peeled from the base material. After that, one or multiple sheets of the compact are stacked and subjected to compression bonding. As a method for the compression bonding, there are given uniaxial pressing, cold isostatic pressing, and hot isostatic pressing. The hot isostatic pressing is desired because a pressure can be applied isotropically and uniformly. It is desired to heat the compact to around the glass transition temperature of the binder during the compression bonding because more satisfactory compression bonding can be achieved. Multiple sheets of the compact can be stacked and subjected to compression bonding so as to achieve a desired thickness. For example, 10 to 100 sheets of the compact can be stacked and then subjected to thermocompression bonding involving applying a pressure of 10 to 60 MPa in a stacking direction over 10 seconds to 10 minutes at 50 to 80° C., to thereby stack the sheets of the compact. Further, multiple sheets of the compact may be aligned and stacked with good accuracy by putting alignment marks on electrodes. It should be appreciated that multiple sheets of the compact may also be stacked with good accuracy by providing a through-hole for positioning in the compact.
In the step (D), it is suitable that the sintering temperature be 1,200° C. or less because a metal having a low melting point and low cost as compared to Pt, such as Ag, Pd, Au, Cu, or Ni, or an alloy thereof may be used. When Ni or Cu is used for the electrode, the sintering in the step (D) is preferably performed in a reducing atmosphere.
In the manufacturing method for a multilayered piezoelectric element according to the present invention, the slurry preferably contains a perovskite-type metal oxide containing at least any one of Ba, Sr, and Ca and Na, Ti, Nb, and Zr. Examples of the perovskite-type metal oxide include sodium niobate, barium titanate, strontium titanate, calcium titanate, barium stannate, strontium stannate, calcium stannate, barium zirconate titanate, strontium zirconate titanate, calcium zirconate titanate, barium stannate titanate, strontium stannate titanate, and calcium stannate titanate. The slurry may contain Cu, and in this case, copper (I) oxide or copper (II) oxide may be used.
The slurry suitably contains copper oxide because the grain growth is accelerated during sintering, and the density of the sintered body increases.
(Liquid Discharge Head)
A liquid discharge head according to the present invention includes at least a liquid chamber having a vibration unit provided with the piezoelectric element or the multilayered piezoelectric element, and a discharge port communicating to the liquid chamber. No particular limitation is imposed on a liquid to be discharged by the liquid discharge head of the present invention as long as the liquid is a fluent material, and the liquid discharge head can discharge an aqueous liquid or a non-aqueous liquid, such as water, ink, or fuel. FIGS. 3A and 3B are schematic views each illustrating a configuration of the liquid discharge head according to an embodiment of the present invention. As illustrated in FIGS. 3A and 3B, the liquid discharge head of the present invention is a liquid discharge head having a piezoelectric element 101 of the present invention. The piezoelectric element 101 includes at least a first electrode 1011, a piezoelectric material 1012, and a second electrode 1013. As illustrated in FIG. 3B, the piezoelectric material 1012 is patterned as necessary. FIG. 3B is a schematic view of the liquid discharge head. The liquid discharge head includes discharge ports 105, individual liquid chambers 102, communicating holes 106 for connecting the individual liquid chambers 102 and the discharge ports 105, liquid chamber partition walls 104, a common liquid chamber 107, a diaphragm 103, and the piezoelectric elements 101. Each of the piezoelectric elements 101, which has a rectangular shape in FIG. 3B, may have a shape except the rectangular shape such as an elliptical shape, a circular shape, or a parallelogram shape. In general, the piezoelectric material 1012 has a shape in conformity with the shape of the individual liquid chamber 102. The vicinity of the piezoelectric element 101 included in the liquid discharge head of the present invention is described in detail with reference to FIG. 3A. FIG. 3A is a sectional view of the piezoelectric element in the width direction of the liquid discharge head illustrated in FIG. 3B. The sectional shape of the piezoelectric element 101, which is illustrated in a rectangular shape, may be a trapezoidal shape or a reverse trapezoidal shape. In FIG. 3A, the first electrode 1011 is used as the lower electrode, and the second electrode 1013 is used as the upper electrode. However, the arrangement of the first electrode 1011 and the second electrode 1013 is not limited to the foregoing. For example, the first electrode 1011 may be used as the lower electrode, or may be used as the upper electrode. Similarly, the second electrode 1013 may be used as the upper electrode, or may be used as the lower electrode. In addition, a buffer layer 108 may be present between the diaphragm 103 and the lower electrode. Note that, those differences in name depend on a manufacturing method for the device and an effect of the present invention can be obtained in any case. In the liquid discharge head, the diaphragm 103 vertically fluctuates owing to the expansion and contraction of the piezoelectric material 1012 to apply a pressure to liquid in the individual liquid chamber 102. As a result, the liquid is discharged from the discharge port 105. The liquid discharge head of the present invention can be used in a printer application or the manufacture of an electronic device. The diaphragm 103 has a thickness of 1.0 μm or more to 15 μm or less, preferably 1.5 μm or more to 8 μm or less. A material for the diaphragm 103, which is not limited, is preferably Si. Si for the diaphragm 103 may be doped with boron or phosphorus. In addition, the buffer layer and the electrode layer on the diaphragm 103 may serve as part of the diaphragm 103. The buffer layer 108 has a thickness of 5 nm or more to 300 nm or less, preferably 10 nm or more to 200 nm or less. The size of the discharge port 105 is 5 μm or more to 40 μm or less in terms of an equivalent circular diameter. The shape of the discharge port 105 may be a circular shape, or may be a star shape, a square shape, or a triangular shape.
(Liquid Discharge Device)
Next, a liquid discharge device of the present invention is described. The liquid discharge device of the present invention includes a conveyance unit for a recording medium and the liquid discharge head.
As an example of the liquid discharge device of the present invention, there may be given an ink jet recording device illustrated in FIGS. 4 and 5. FIG. 5 illustrates a liquid discharge device (ink jet recording device) 881 illustrated in FIG. 4 in a state in which sheathings 882 to 885 and 887 thereof are removed. The ink jet recording device 881 includes an automatic sheet feeder unit 897 for automatically feeding recording sheets as recording media into a device main body 896. Further, the ink jet recording device 881 includes a conveyance unit 899 for guiding the recording sheet fed from the automatic sheet feeder unit 897 to a predetermined recording position and from the recording position to an output port 898, a recording unit 891 for performing recording on the recording sheet conveyed to the recording position, and a recovery unit 890 for performing a recovery process on the recording unit 891. The recording unit 891 includes a carriage 892 that contains the liquid discharge head of the present invention and is reciprocated on a rail.
In such ink jet recording device, the carriage 892 is moved on the rail based on an electric signal sent from a computer, and a drive voltage is applied to electrodes sandwiching a piezoelectric material so that the piezoelectric material is displaced. This displacement of the piezoelectric material pressurizes each individual liquid chamber 102 via the diaphragm 103 illustrated in FIG. 3B, and hence ink is discharged from the discharge port 105 so as to perform printing. The liquid discharge device of the present invention can discharge liquid uniformly at high speed, and hence the device can be downsized.
In the example described above, the printer is exemplified. However, the liquid discharge device of the present invention can be used as a printing device such as an ink jet recording device including a facsimile, a multifunction peripheral, a copying machine, and the like, or as an industrial liquid discharge device or a drawing apparatus for an object.
(Ultrasonic Motor)
An ultrasonic motor according to the present invention includes at least a vibration body provided with the piezoelectric element or the multilayered piezoelectric element, and a moving body to be brought into contact with the vibration body. FIGS. 6A and 6B are schematic views each illustrating a configuration of the ultrasonic motor according to an embodiment of the present invention. FIG. 6A illustrates the ultrasonic motor in which the piezoelectric element of the present invention is formed of a single plate. The ultrasonic motor includes an oscillator 201, a rotor 202, which is brought into contact with the sliding surface of the oscillator 201 with a pressure applied from a pressurizing spring (not shown), and an output shaft 203 provided so as to be integral with the rotor 202. The oscillator 201 is formed of a metal elastic ring 2011, a piezoelectric element 2012 of the present invention, and an organic adhesive 2013 for bonding the piezoelectric element 2012 to the elastic ring 2011 (such as an epoxy- or cyanoacrylate-based adhesive). The piezoelectric element 2012 of the present invention is formed of a piezoelectric material sandwiched between a first electrode (not shown) and a second electrode (not shown). The application of two alternating voltages different from each other in phase by n/2 to the piezoelectric element of the present invention results in the generation of a flexural traveling wave in the oscillator 201, and hence each point on the sliding surface of the oscillator 201 undergoes an elliptical motion. When the rotor 202 is brought into press contact with the sliding surface of the oscillator 201, the rotor 202 receives a frictional force from the oscillator 201 to rotate in the direction opposite to the flexural traveling wave. A body to be driven (not shown) is joined to the output shaft 203, and is driven by the rotary force of the rotor 202. The application of a voltage to the piezoelectric material results in the expansion and contraction of the piezoelectric material due to a transverse piezoelectric effect. When an elastic body such as a metal is joined to the piezoelectric element, the elastic body is bent by the expansion and contraction of the piezoelectric material. The ultrasonic motor of the kind described here utilizes this principle. Next, an ultrasonic motor including a piezoelectric element having a multilayered structure is illustrated in FIG. 6B. An oscillator 204 is formed of a multilayered piezoelectric element 2042 sandwiched between tubular metal elastic bodies 2041. The multilayered piezoelectric element 2042 is an element formed of multiple stacked piezoelectric materials (not shown), and includes a first electrode and a second electrode on its outer surfaces of the stack, and internal electrodes on its inner surface of the stack. The metal elastic bodies 2041 are fastened with bolts so that the piezoelectric element 2042 may be sandwiched between and fixed by the bodies. Thus, the oscillator 204 is formed. The application of alternating voltages different from each other in phase to the piezoelectric element 2042 causes the oscillator 204 to excite two vibrations orthogonal to each other. The two vibrations are combined to form a circular vibration for driving the tip portion of the oscillator 204. Note that, a constricted annular groove is formed in the upper portion of the oscillator 204 to enlarge the displacement of the vibration for driving. A rotor 205 is brought into contact with the oscillator 204 under a pressure from a spring 206 for pressurization to obtain a frictional force for driving. The rotor 205 is rotatably supported by a bearing.
(Optical Device)
Next, an optical device of the present invention is described. The optical device of the present invention includes a drive unit including the ultrasonic motor.
FIGS. 7A and 7B are sectional diagrams of main parts of an interchangeable lens barrel for a single-lens reflex camera as an example of an imaging device according to a preferred embodiment of the present invention. In addition, FIG. 8 is an exploded perspective diagram of the interchangeable lens barrel for the single-lens reflex camera as the example of the imaging device according to the preferred embodiment of the present invention. A fixed barrel 712, a linear guide barrel 713, and a front unit barrel 714 are fixed to an attaching/detaching mount 711 for a camera. These are fixed members of the interchangeable lens barrel.
A linear guide groove 713a in an optical axis direction for a focus lens 702 is formed on the linear guide barrel 713. Cam rollers 717a and 717b protruding outward in a radial direction are fixed to a rear unit barrel 716 supporting the focus lens 702 via axial screws 718, and the cam roller 717a is fitted in the linear guide groove 713a. 
A cam ring 715 is fitted on the inner periphery of the linear guide barrel 713 in a rotatable manner. Relative movement between the linear guide barrel 713 and the cam ring 715 in the optical axis direction is restricted because a roller 719 fixed to the cam ring 715 is fitted in an annular groove 713b of the linear guide barrel 713. A cam groove 715a for the focus lens 702 is formed on the cam ring 715, and the above-mentioned cam roller 717b is simultaneously fitted in the cam groove 715a. 
On the outer peripheral side of the fixed barrel 712, there is disposed a rotation transmission ring 720 supported by a ball race 727 in a rotatable manner at a constant position with respect to the fixed barrel 712. The rotation transmission ring 720 has shafts 720f extending radially from the rotation transmission ring 720, and rollers 722 are supported by the shafts 720f in a rotatable manner. A large diameter part 722a of the roller 722 is brought into contact with a mount side end surface 724b of a manual focus ring 724. In addition, a small diameter part 722b of the roller 722 is brought into contact with a joining member 729. Six rollers 722 are disposed on the outer periphery of the rotation transmission ring 720 at uniform intervals, and each roller is provided in the relationship as described above.
A low friction sheet (washer member) 733 is disposed on an inner diameter part of the manual focus ring 724, and this low friction sheet is sandwiched between a mount side end surface 712a of the fixed barrel 712 and a front side end surface 724a of the manual focus ring 724. In addition, an outer diameter surface of the low friction sheet 733 is formed in a ring shape so as to be circumferentially fitted on an inner diameter part 724c of the manual focus ring 724. Further, the inner diameter part 724c of the manual focus ring 724 is circumferentially fitted on an outer diameter part 712b of the fixed barrel 712. The low friction sheet 733 has a role of reducing friction in a rotation ring mechanism in which the manual focus ring 724 rotates relatively to the fixed barrel 712 about the optical axis.
Note that, the large diameter part 722a of the roller 722 is brought into contact with the mount side end surface 724a of the manual focus ring in a state in which a pressure is applied by a pressing force of a waved washer 726 pressing an ultrasonic motor 725 to the front of the lens. In addition, similarly, the small diameter part 722b of the roller 722 is brought into contact with the joining member 729 in a state in which an appropriate pressure is applied by a pressing force of the waved washer 726 pressing the ultrasonic motor 725 to the front of the lens. Movement of the waved washer 726 in the mount direction is restricted by a washer 732 connected to the fixed barrel 712 by bayonet joint. A spring force (biasing force) generated by the waved washer 726 is transmitted to the ultrasonic motor 725, and further to the roller 722, to be a force for the manual focus ring 724 to press the mount side end surface 712a of the fixed barrel 712. In other words, the manual focus ring 724 is integrated in a state in which the manual focus ring 724 is pressed to the mount side end surface 712a of the fixed barrel 712 via the low friction sheet 733.
Therefore, when a control unit (not shown) drives the ultrasonic motor 725 to rotate with respect to the fixed barrel 712, the rollers 722 rotate about the shafts 720f because the joining member 729 is brought into frictional contact with the small diameter parts 722b of the rollers 722. As a result of the rotation of the rollers 722 about the shafts 720f, the rotation transmission ring 720 rotates about the optical axis (automatic focus operation).
In addition, when a manual operation input portion (not shown) gives a rotation force about the optical axis to the manual focus ring 724, the rollers 722 rotate about the shafts 720f by friction force because the mount side end surface 724b of the manual focus ring 724 is brought into contact by pressure to the large diameter parts 722a of the rollers 722. When the large diameter parts 722a of the rollers 722 rotate about the shafts 720f, the rotation transmission ring 720 rotates about the optical axis. In this case, the ultrasonic motor 725 does not rotate because of a friction retaining force between a rotor 725c and a stator 725b (manual focus operation).
Two focus keys 728 are mounted to the rotation transmission ring 720 at opposing positions, and the focus key 728 is fitted to a notch portion 715b disposed on the tip of the cam ring 715. Therefore, when the automatic focus operation or the manual focus operation is performed so that the rotation transmission ring 720 is rotated about the optical axis, the rotation force is transmitted to the cam ring 715 via the focus key 728. When the cam ring is rotated about the optical axis, the rear unit barrel 716 whose rotation is restricted by the cam roller 717a and the linear guide groove 713a is moved forward and backward along the cam groove 715a of the cam ring 715 by the cam roller 717b. Thus, the focus lens 702 is driven, and the focus operation is performed.
In this case, the interchangeable lens barrel for the single-lens reflex camera is described above as the optical device of the present invention, but the present invention can be applied to any optical device including the drive unit including the ultrasonic motor, regardless of a type of the camera, including a compact camera, an electronic still camera, a personal digital assistant with camera, and the like.
(Vibration Device and Dust Removing Device)
A vibration device used for conveying or removing particles, powder, or liquid droplets is used widely for an electronic device or the like.
Next, as an example of the vibration device of the present invention, a dust removing device using the piezoelectric element of the present invention is described.
A dust removing device according to the present invention includes a vibration body provided with the piezoelectric element and the multilayered piezoelectric element on a diaphragm.
FIGS. 9A and 9B are schematic views each illustrating a dust removing device according to an embodiment of the present invention. A dust removing device 310 is formed of a plate-like piezoelectric element 330 and a diaphragm 320. The piezoelectric element 330 may be the multilayered piezoelectric element of the present invention. The material of the diaphragm 320 is not limited. In the case where the dust removing device 310 is used for an optical device, a transparent material or a reflective material can be used as the material of the diaphragm 320.
FIGS. 10A to 10C are schematic views each illustrating a configuration of the piezoelectric element 330 illustrated in FIGS. 9A and 9B. FIGS. 10A and 10C illustrate a front surface configuration and a rear surface configuration of the piezoelectric element 330, respectively. FIG. 10B illustrates a side surface configuration thereof. As illustrated in FIGS. 9A and 9B, the piezoelectric element 330 includes a piezoelectric material 331, a first electrode 332, and a second electrode 333. The first electrode 332 and the second electrode 333 are disposed so as to be opposed to each other on the plate planes of the piezoelectric material 331. Similarly to FIGS. 9A and 9B, the piezoelectric element 330 may be the multilayered piezoelectric element of the present invention. In this case, the piezoelectric material 331 has an alternate structure of a piezoelectric material layer and an internal electrode and can provide driving waveforms different from each other in phase depending on the piezoelectric material layers by short-circuiting the internal electrode with the first electrode 332 or the second electrode 333 alternately. The front plane of the piezoelectric element 330 illustrated in FIG. 10C, on which the first electrode 332 is disposed, is referred to as a first electrode plane 336. The front plane of the piezoelectric element 330 illustrated in FIG. 10A, on which the second electrode 333 is disposed, is referred to as a second electrode plane 337.
In this case, the electrode plane in the present invention means a plane of the piezoelectric element on which the electrode is disposed. For example, as illustrated in FIGS. 10A to 10C, the first electrode 332 may extend around to the second electrode plane 337.
As illustrated in FIGS. 9A and 9B, as for the piezoelectric element 330 and the diaphragm 320, the plate surface of the diaphragm 320 is fixed to the first electrode plane 336 of the piezoelectric element 330. When the piezoelectric element 330 is driven, a stress is generated between the piezoelectric element 330 and the diaphragm 320 so that out-of-plane oscillation is generated in the diaphragm. The dust removing device 310 of the present invention is a device that removes foreign matters such as dust sticking to the surface of the diaphragm 320 by the out-of-plane oscillation of the diaphragm 320. The out-of-plane oscillation means elastic oscillation in which the diaphragm is displaced in the optical axis direction, namely in the thickness direction of the diaphragm.
FIGS. 11A and 11B are schematic views illustrating a vibration principle of the dust removing device 310 of the present invention. FIG. 11A illustrates a state in which alternating electric fields having the same phase are applied to a pair of left and right piezoelectric elements 330 so that the out-of-plane oscillation is generated in the diaphragm 320. The polarization direction of the piezoelectric material forming the pair of left and right piezoelectric elements 330 is the same as the thickness direction of the piezoelectric elements 330, and the dust removing device 310 is driven by the seventh oscillation mode. FIG. 11B illustrates a state in which alternating voltages having reverse phases by 180 degrees are applied to the pair of left and right piezoelectric elements 330 so that the out-of-plane oscillation is generated in the diaphragm 320. The dust removing device 310 is driven by the sixth oscillation mode. The dust removing device 310 of the present invention is a device that can effectively remove dust sticking to the surface of the diaphragm by using at least two oscillation modes selectively.
(Imaging Device)
Next, an imaging device of the present invention is described. The imaging device of the present invention is an imaging device including at least the dust removing device and an imaging element unit and is characterized in that the diaphragm of the dust removing device is provided on a light receiving plane side of the imaging element unit. FIGS. 12 and 13 are diagrams each illustrating a digital single-lens reflex camera as an example of an imaging device according to a preferred embodiment of the present invention.
FIG. 12 is a front side perspective diagram of a camera main body 601 viewed from an object side, in which an imaging lens unit is removed. FIG. 13 is an exploded perspective diagram illustrating an internal schematic configuration of the camera for describing a peripheral structure of the dust removing device and an imaging unit 400 of the present invention.
A mirror box 605 for guiding an imaging light beam that has passed through the imaging lens is disposed in the camera main body 601, and a main mirror (quick return mirror) 606 is disposed in the mirror box 605. The main mirror 606 can take one of states including a state of being supported at an angle of 45 degrees with respect to an imaging optical axis in order to guide the imaging light beam in the direction to a penta-dach mirror (not shown) and a state of being retreated from the imaging light beam in order to guide the imaging light beam in the direction to an imaging element (not shown).
On the object side of a main body chassis 300 to be a skeleton of the camera main body, the mirror box 605 and a shutter unit 200 are disposed in order from the object side. In addition, on a photographer side of the main body chassis 300, the imaging unit 400 is disposed. The imaging unit 400 is adjusted and disposed so that the imaging surface of the imaging element is parallel to a mounting surface of a mount portion 602 to be a reference for mounting the imaging lens unit with a predetermined distance.
In this case, the digital single-lens reflex camera is described above as the imaging device of the present invention, but the device may be a camera with interchangeable imaging lens unit such as a mirrorless digital single-lens camera without the mirror box 605, for example. In addition, the present invention can be applied to various types of imaging devices or electronic and electric devices including the imaging device, such as a video camera with interchangeable imaging lens unit, a copying machine, a facsimile, and a scanner, in particular, a device that is required to remove dust sticking to a surface of an optical component.
(Electronic Device)
Next, an electronic device of the present invention is described. The electronic device of the present invention includes a piezoelectric acoustic component including the piezoelectric element or the multilayered piezoelectric element. Examples of the piezoelectric acoustic component include a speaker, a buzzer, a microphone, and a surface acoustic wave (SAW) element.
FIG. 14 is a general perspective diagram of a main body 931 of a digital camera as an example of an electronic device according to a preferred embodiment of the present invention, as viewed from the front. On a front surface of the main body 931, there are disposed an optical device 901, a microphone 914, a stroboscopic light emission unit 909, and a fill light unit 916. Because the microphone 914 is installed in the main body, the microphone 914 is illustrated by a broken line. In the front of the microphone 914, there is a hole shape provided for collecting external sound.
A power button 933, a speaker 912, a zoom lever 932, and a release button 908 for performing a focus operation are disposed on the top surface of the main body 931. The speaker 912 is installed in the main body 931 and is illustrated by a broken line. In the front of the speaker 912, there is a hole shape provided for transmitting sound to the outside.
The piezoelectric acoustic component of the present invention is used for at least one of the microphone 914, the speaker 912, and the surface acoustic wave element.
In this case, the digital camera is described above as the electronic device of the present invention, but the present invention can also be applied to various types of the electronic device including the piezoelectric acoustic component, such as a sound reproduction device, a sound recording device, a mobile phone, or an information terminal.
As described above, the piezoelectric element and the multilayered piezoelectric element of the present invention can be preferably used in a liquid discharge head, a liquid discharge device, an ultrasonic motor, an optical device, a vibration device, a dust removing device, an imaging device, and an electronic device. Through the use of the piezoelectric element and the multilayered piezoelectric element of the present invention, it is possible to provide the liquid discharge head having the same or higher nozzle density and discharge speed than the case where the piezoelectric element containing lead is used.
Through the use of the liquid discharge head of the present invention, it is possible to provide the liquid discharge device having the same or higher discharge speed and discharge accuracy than the case where the piezoelectric element containing lead is used. Through the use of the piezoelectric element and the multilayered piezoelectric element of the present invention, it is possible to provide the ultrasonic motor having the same or higher driving force and durability than the case where the piezoelectric element containing lead is used.
Through the use of the ultrasonic motor of the present invention, it is possible to provide the optical device having the same or higher durability and operation accuracy than the case where the piezoelectric element containing lead is used.
Through the use of the piezoelectric element and the multilayered piezoelectric element of the present invention, it is possible to provide the vibration device having the same or higher vibration performance and durability than the case where the piezoelectric element containing lead is used.
Through the use of the vibration device of the present invention, it is possible to provide the dust removing device having the same or higher dust-removing efficiency and durability than the case where the piezoelectric element containing lead is used.
Through the use of the dust removing device of the present invention, it is possible to provide the imaging device having the same or higher dust-removing function than the case where the piezoelectric element containing lead is used.
Through the use of the piezoelectric acoustic component including the piezoelectric element or the multilayered piezoelectric element of the present invention, it is possible to provide the electronic device having the same or higher sound producing performance than the case where the piezoelectric element containing lead is used.
The piezoelectric material of the present invention can be used in such a device as an ultrasonic oscillator, a piezoelectric actuator, a piezoelectric sensor, and a ferroelectric memory, as well as the liquid discharge head and the motor.
EXAMPLES
Hereinafter, the piezoelectric material of the present invention is described more specifically by way of examples. However, the present invention is not limited by the following examples.
Table 1 shows compositions of sintered bodies of Examples 1 to 22 of the present invention and Comparative Examples 1 to 14.














TABLE 1





Sample
M
x/y
y
z
w
v
Cu (%)






















Comparative Example 1
Ba
0.96
0.90
0
0
0
0.00


Example 1
Ba
0.96
0.89
0.01
0
0
0.45


Example 2
Ba
0.96
0.89
0.01
0
0.02
0.50


Example 3
Ba
0.97
0.89
0.01
0
0.05
0.50


Example 4
Ba
0.97
0.89
0.01
0
0.1
0.50


Comparative Example 2
Ba
0.97
0.89
0.01
0
0.2
0.50


Example 5
Ba
0.97
0.89
0.01
0.02
0
0.50


Example 6
Ba
0.97
0.89
0.01
0.05
0
0.50


Example 7
Ba
0.97
0.89
0.01
0.1
0
0.50


Comparative Example 3
Ba
0.97
0.89
0.01
0.2
0
0.50


Example 8
Ba
0.97
0.89
0.01
0.02
0.02
0.50


Example 9
Ba
0.97
0.89
0.01
0.05
0.05
0.50


Comparative Example 4
Ba
0.98
0.88
0
0
0
0.00


Comparative Example 5
Ba
0.98
0.88
0
0
0
0.44


Comparative Example 6
Ba
0.98
0.88
0
0.03
0
0.44


Comparative Example 7
Ba
0.98
0.88
0
0.06
0
0.44


Comparative Example 8
Ba
0.98
0.88
0
0.1
0
0.44


Comparative Example 9
Ba
0.98
0.88
0
0.2
0
0.44


Example 10
Ba
0.98
0.88
0.005
0
0
0.44


Example 11
Ba
0.98
0.87
0.01
0
0
0.00


Example 12
Ba
0.98
0.87
0.01
0
0
0.44


Example 13
Ba
0.98
0.86
0.02
0
0
0.44


Example 14
Ba
0.98
0.85
0.03
0
0
0.44


Comparative Example 10
Ba
0.98
0.83
0.06
0
0
0.44


Comparative Example 11
Ba
0.98
0.79
0.1
0
0
0.44


Comparative Example 12
Ba
0.98
0.70
0.2
0
0
0.44


Example 15
0.92Ba + 0.08Sr
0.98
0.87
0.01
0
0
0.44


Example 16
0.85Ba + 0.15Sr
0.98
0.86
0.02
0
0
0.44


Example 17
0.80Ba + 0.20Sr
0.98
0.85
0.03
0
0
0.44


Example 18
0.92Ba + 0.08Ca
0.98
0.87
0.01
0
0
0.44


Example 19
0.85Ba + 0.15Ca
0.98
0.86
0.02
0
0
0.44


Example 20
0.80Ba + 0.20Ca
0.98
0.85
0.03
0
0
0.44


Example 21
0.85Ba + 0.075Sr + 0.075Ca
0.99
0.86
0.02
0
0
0.44


Comparative Example 13
Ba
0.98
0.85
0
0
0
0.00


Example 22
Ba
0.98
0.84
0.01
0
0
0.42


Comparative Example 14
Ba
1.01
0.84
0.01
0
0
0.42









Raw materials were weighed so that x, y, M, z, w, and v in the general formula (1): (NaxM1-y)(Zrz(Nb1-wTaw)y(Ti1-vSnv)(1-y-z))O3 represented values as shown in Table 1, and Cu was weighed as an amount with respect to 1 mol of the perovskite-type metal oxide represented by the general formula (1). The raw material powders were mixed in a ball mill for 12 hours.
As the raw materials in Comparative Examples 1, 2, 4, 5, and 10 to 13, and Examples 1 to 4 and 10 to 22, sodium niobate (NaNbO3) powder having a purity of 99% or more, barium carbonate (BaCO3) powder having a purity of 99.95%, strontium carbonate (SrCO3) powder having a purity of 99.99%, calcium carbonate (CaCO3) powder having a purity of 99.99%, zirconium oxide (ZrO2) powder having a purity of 98%, barium stannate (BaSnO3) powder having a purity of 99% or more, barium titanate (BaTiO3) powder having a purity of 99% or more, and copper oxide (CuO(II)) powder having a purity of 99.9% were used.
As the raw material in Comparative Example 14, sodium carbonate (Na2CO3) powder having a purity of 99% was used in addition to the raw materials used in Example 22.
As the raw materials in Comparative Examples 3 and 6 to 9, and Examples 5 to 9, sodium niobate (NaNbO3) powder having a purity of 99% or more, barium carbonate (BaCO3) powder having a purity of 99.95%, zirconium oxide (ZrO2) powder having a purity of 98%, barium stannate (BaSnO3) powder having a purity of 99% or more, barium titanate (BaTiO3) powder having a purity of 99% or more, copper oxide (CuO) powder having a purity of 99.9%, sodium carbonate (Na2CO3) powder having a purity of 99%, and tantalum oxide (Ta2O5) powder having a purity of 99.9% were used.
The mixed powder was calcined at 900 to 1,100° C. in the air for 2 to 5 hours. The calcined powder was crushed, and a PVB binder was added thereto in an amount of 3 wt % with respect to the weight of the calcined powder, followed by granulation. The granulated powder was filled in a mold and was compressed under a pressure of 200 MPa to manufacture a compact having a diameter of 17 mm and a thickness of about 1 mm. By sintering the obtained compact at 1,150 to 1,300° C. in the air for 2 to 6 hours, a sintered body was obtained.
The density of the sintered body was measured by Archimedes method and the relative density was calculated. As a result, it was found that the relative density of any of the sintered bodies was 94% or more. In the samples of the present invention, the relative density of a sample with Cu added thereto was higher than that of a sample without Cu added thereto having the same composition as that of the sample with Cu added thereto. When Cu was added, the temperatures required for calcination and sintering were decreased by 50° C. to 100° C. compared to the case where Cu was not added.
The sintered body was polished so that the thickness was about 0.5 mm. X-ray diffraction was carried out on the polished sintered body or powder obtained by crushing the polished sintered body to evaluate the constituent phase and the lattice constant. The X-ray diffraction confirmed that the sample was substantially of a perovskite structure single phase.
The composition of the sintered body was evaluated by inductively coupled plasma optical emission spectrometry (ICP), and the molar number of Na with respect to the sum of the molar numbers of Nb and Ta (Na/(Nb+Ta)) fell within a range of 96 to 99% in all the samples excluding Comparative Example 14. Thus, Na was deficient. The content of Cu was small, and hence the values shown in Table 1 include a measurement error of ±50%. The grain size in the sintered body was observed and evaluated with an optical microscope or an electron microscope.
The grain size of the sintered body was observed with an electron microscope. As a result, it was found that the grain size fell within a range of 2 to 50 μm.
The distribution of Cu in the sintered body was examined by energy dispersive X-ray spectroscopy, and a great amount of the added Cu was present at the grain boundary between the grains and a small amount of the Cu was present in the particles.
In order to evaluate electric characteristics such as piezoelectric property and insulation resistance, piezoelectric elements of Examples 1 to 22 were produced. First, in order to remove the stress in the polished sintered body and an organic component on the surface of the sintered body, the sintered body was subjected to heat treatment at 400 to 500° C. in the air for 30 minutes. Gold electrodes each having a thickness of 400 nm were formed on front and rear surfaces of the disc-shaped ceramics by DC sputtering. Titanium was formed into a film having a thickness of 30 nm as a contact layer between the electrodes and the ceramics. The ceramics with the electrodes was cut to a strip-shaped piezoelectric element having a length of 10 mm, a width of 2.5 mm, and a thickness of 0.5 mm.
For evaluating a resistivity, a semiconductor parameter analyzer was used. A DC voltage of several ten volts to 100 volts was applied to a sample, and the resistance after 30 seconds from the beginning of the application of the voltage was measured. The resistivity was calculated from the measured resistance and the dimensions of the sample.
The polarization-electric field hysteresis measurement was conducted so as to determine the presence/absence of ferroelectricity in a practical electric field of a target element at room temperature. A material exhibiting the ferroelectricity in a predetermined temperature region can be considered to have piezoelectricity in the same temperature region, and can also be used as a memory material. Specifically, the polarization amount obtained by applying an alternating electric field (triangular wave) to the piezoelectric element of the present invention was measured. The frequency of the alternating electric field was set to 10 to 100 Hz. The intensity of the electric field was at maximum about ±50 kV/cm.
Prior to the evaluation of the piezoelectric property, polarization treatment was performed. Specifically, a voltage of 1.5 to 5 kV/mm was applied to a sample for 30 minutes in an oil bath held at 150° C. While the voltage was applied to the sample, the sample was cooled to room temperature. In Comparative Example 14, the insulation resistance was low, and hence the polarization treatment was not able to be performed.
The Young's modulus (Y11), the electromechanical coupling coefficient (k31), the piezoelectric constant (d31), and the electromechanical quality factor (Qm) of a d31 element formed in the shape of a strip were measured by a resonance-antiresonance method. The piezoelectric constant (d33) was evaluated with a d33 meter based on Berlin court through use of the sample. For measurement of a relative dielectric constant, an impedance analyzer was used. The relative dielectric constant shown herein is a value at a measurement frequency of 1 kHz unless otherwise specified, and the magnitude of an applied alternating electric field was set to 500 mV. The measurement was conducted after the polarization treatment. When the temperature dependence of a relative dielectric constant was evaluated, the measurement of a relative dielectric constant was started from room temperature. The sample was cooled from room temperature to −100° C. temporarily, and thereafter, heated to 350° C. A change in relative dielectric constant at this time was recorded. The Curie temperature and successive phase transition temperature were calculated from a local maximum portion of the relative dielectric constant.
Tables 2 and 3 show characteristics of typical samples.














TABLE 2






Curie

Electromechanical
Piezoelectric
Young's
Electrochemical
Piezoelectric



temperature
Relative dielectric
coupling
constant
modulus
quality factor
constant


Sample
(° C.)
constant (—)
coefficient k31 (—)
d31 (pC/N)
Y11 (Gpa)
Qm (—)
d33 (pC/N)






















Comparative Example 1
240
934
0.18
49.1
121
176
145


Comparative Example 6
190
917
0.16
43.2
127
277
120


Comparative Example 15
160
1,096
0.16
41.6
132
288
122


Example 10
180
953
0.18
44.1
131
254
132


Example 11
170
977
0.17
45.8
132
260
136


Example 12
160
1,040
0.18
48.0
129
407
156


Example 13
130
1,335
0.18
55.1
128
444
178


Example 14
100
2,099
0.12
46.1
118
302
157


Example 15
160
1,073
0.18
49.4
131
407
160


Example 16
130
1,429
0.17
53.3
130
407
174


Example 17
100
2,267
0.14
55.7
128
323
188


Example 18
160
1,055
0.18
48.4
130
382
140


Example 19
140
1,317
0.17
49.8
130
300
166


Example 20
90
2,174
0.14
54.7
127
211
207



















TABLE 3







Composition
Resistivity (GΩ · cm)



















Comparative Example 6
5.0



Example 10
6.8



Example 12
34.2



Example 13
167.5



Example 14
266.7



Comparative Example 12
125.2



Comparative Example 13
7.6



Comparative Example 14
1.6










(Piezoelectric Materials and Piezoelectric Elements of Examples 1 to 22)
Examples 1 to 22 are samples each having NN—BT as a basic composition in which part of the B site is replaced by Zr. Compared to Comparative Examples 1, 4, 5, and 13 in which part of the B site is not replaced by Zr, the relative dielectric constant increased and the piezoelectric constant d31 or d33 increased in each of Examples 1 to 22 through the replacement by Zr. On the other hand, in each of Examples 1 to 22, the Curie temperature, electrochemical coupling coefficient, Young's modulus, and electromechanical quality factor decreased (Table 2).
The resistivity of the sample continued to increase until 3% of the B site was replaced by Zr. However, after 3% of the B site was replaced by Zr, the resistivity started decreasing (Table 3).
The piezoelectric constant of the sample was further enhanced, and the electromechanical quality factor was increased by adding Cu to piezoelectric ceramics in addition to the replacement by Zr (Table 2). As the replacement amount of Zr increased, the coercive field obtained by the polarization-electric field hysteresis measurement decreased. FIG. 15 shows polarization-electric field hysteresis loops of the sintered bodies of Comparative Example 5, Example 10, Example 12, Example 13, and Example 14, and the coercive field decreased in the stated order.
Examples 2 to 4, 8, and 9, and Comparative Example 2
In the case where Sn occupied part of the B site, the Curie temperature and the successive phase transition temperature were able to be adjusted in accordance with the amount of Sn. When Sn corresponding to 10% of Ti was added, the Curie temperature decreased by 30° C., and the successive phase transition temperature increased by about 30° C.
In the case where Sn in an amount corresponding to 10% of Ti was included (Example 4), the temperature range in which the perovskite-type metal oxide of the present invention was tetragonal was about 150° C. As the amount of Sn decreased, the temperature range in which the perovskite-type metal oxide of the present invention was tetragonal increased. In the case where Sn was not included, the temperature range in which NN—BT was tetragonal was 200° C. or more. Further, in the case where Sn in an amount corresponding to 20% of Ti was included (Comparative Example 2), the Curie temperature was less than 150° C.
Examples 5 to 9, and Comparative Examples 3 and 6 to 9
In the case where Ta occupied part of the B site, the Curie temperature and the successive phase transition temperature were able to be adjusted in accordance with the amount of Ta. When Ta corresponding to 10% of Nb was added, the Curie temperature decreased by 60° C., and the successive phase transition temperature decreased to −100° C. or less (Example 7). In the case where Ta occupied part of the B site, when the amount of Ta was reduced, the sintering temperature decreased. When Ta corresponding to 10% of Nb was reduced, the sintering temperature decreased by about 100° C. In the case where Zr was not included, and Ta occupied part of the B site, although the Curie temperature decreased in accordance with the amount of Ta, the dielectric constant at room temperature was not enhanced, with the result that there was no effect of improving piezoelectric performance (Comparative Examples 6 to 9).
Example 90
Raw materials corresponding to Example 12 were weighed in a manner described below.
Sodium carbonate (Na2CO3) powder, niobium oxide (Nb2O5) powder, barium titanate (BaTiO3) powder, barium zirconate (BaZrO3) powder, and copper oxide (CuO) powder were weighed so that Na, Nb, Ba, Zr, and Cu achieved the composition of Example 12 shown in Table 1. The weighed raw material powders were mixed, and mixed in a ball mill overnight.
A solvent, a binder (PVB), and a plasticizer (dibutyl phthalate) were added to the mixed powder to prepare a slurry. The slurry was formed into a sheet by a doctor blade method to obtain a green sheet having a thickness of 50 μm.
A conductive paste for an internal electrode was printed on the green sheet. As the conductive paste, an Ag70%-Pd30% alloy (Ag/Pd=2.33) paste was used. Nine green sheets coated with the conductive paste were stacked, and the multilayered body was sintered under the condition of 1,150° C. for 5 hours to obtain a sintered body. The sintered body was cut to a size of 10 mm×2.5 mm, and thereafter side surfaces thereof were polished. A pair of external electrodes (first electrode and second electrode) for short-circuiting the internal electrodes alternately was formed by Au sputtering to produce a multilayered piezoelectric element as illustrated in FIG. 2B.
The internal electrodes of the obtained multilayered piezoelectric element were observed. As a result, it was found that Ag—Pd as an electrode material and a piezoelectric material were formed alternately.
The sample was subjected to polarization treatment prior to the evaluation of piezoelectricity. Specifically, the sample was heated to 150° C. in an oil bath, and a voltage of 2 kV/mm was applied between the first electrode and the second electrode for 30 minutes. While the voltage was applied, the sample was cooled to room temperature.
The piezoelectricity of the thus obtained multilayered piezoelectric element was evaluated. As a result, it was found that the multilayered piezoelectric element had sufficient insulation property. Accordingly, the satisfactory piezoelectric property equal to that of the piezoelectric material of Example 12 was obtained.
Example 91
Sodium niobate (NaNbO3) powder, barium titanate (BaTiO3) powder, and barium zirconate (BaZrO3) powder were weighed so that Na, Nb, Ba, and Zr had the compositions described in Example 11 in Table 1. The weighed raw material powders were mixed overnight with a ball mill. A solvent, a binder (PVB), and a plasticizer (dibutyl phthalate) were added to the mixed powder to prepare a slurry. The slurry was formed into a sheet by a doctor blade method to obtain a green sheet having a thickness of 50 μm.
A conductive paste for an internal electrode was printed on the green sheet. As the conductive paste, an Ni paste was used. Nine green sheets coated with the conductive paste were stacked, and the multilayered body was subjected to thermocompression bonding.
The multilayered body subjected to thermocompression bonding was sintered in a tubular furnace. The sintering was performed in the atmosphere up to 300° C. to remove the binder. After that, the atmosphere was changed to a reducing atmosphere (H2:N2=2.98, oxygen concentration: 2×10−6 Pa) and held at 1,200° C. for 5 hours. In the temperature decrease step, the oxygen concentration was changed to 30 Pa at 1,000° C. or less, and the multilayered body was cooled to room temperature.
The thus obtained sintered body was cut to a size of 10 mm×2.5 mm, and side surfaces thereof were polished. A pair of external electrodes (first electrode and second electrode) for short-circuiting internal electrodes alternately was formed by Au sputtering to produce a multilayered piezoelectric element as illustrated in FIG. 3B.
The internal electrodes of the obtained multilayered piezoelectric element were observed. As a result, it was found that Ni as an electrode material (electrode layer) and a piezoelectric material layer were formed alternately. The obtained multilayered piezoelectric element was subjected to polarization treatment by applying an electric field of 2 kV/mm to the multilayered piezoelectric element in an oil bath held at 150° C. for 30 minutes. The piezoelectric property of the obtained multilayered piezoelectric element was evaluated. As a result, sufficient insulation property was obtained, and satisfactory piezoelectric property equivalent to that of the piezoelectric element of Example 11 was obtained.
Example 100
Through the use of the piezoelectric element of Example 12, the liquid discharge head illustrated in FIGS. 3A and 3B was manufactured. It was confirmed that ink was discharged in accordance with an input electric signal.
Example 101
Through the use of the liquid discharge head of Example 100, the liquid discharge device illustrated in FIG. 4 was manufactured. It was confirmed that ink was discharged on and adhered to a recording medium in accordance with an input electric signal.
Example 102
Through the use of the piezoelectric element of Example 12, the ultrasonic motor illustrated in FIG. 6A was manufactured. It was confirmed that the motor rotated in accordance with an applied voltage.
Example 103
Through the use of the ultrasonic motor of Example 102, the optical device illustrated in FIGS. 7A and 7B was manufactured. It was confirmed that the automatic focus operation was performed in accordance with an applied alternating voltage.
Example 104
Through the use of the piezoelectric element of Example 12, the dust removing device illustrated in FIGS. 9A and 9B was manufactured. Plastic beads were scattered, and an alternating voltage was applied. Then, it was confirmed that satisfactory dust removing efficiency was exhibited.
Example 105
Through the use of the dust removing device of Example 104, the imaging device illustrated in FIG. 12 was manufactured. During operation, the dust on the surface of the imaging unit was satisfactorily removed, and an image without a dust defect was obtained.
Example 106
Through the use of the multilayered piezoelectric element of each of Examples 90 and 91, the liquid discharge head illustrated in FIGS. 3A and 3B was manufactured. It was confirmed that ink was discharged in accordance with an input electric signal.
Example 107
Through the use of the liquid discharge head of Example 106, the liquid discharge device illustrated in FIG. 4 was manufactured. It was confirmed that ink was discharged on and adhered to a recording medium in accordance with an input electric signal.
Example 108
Through the use of the multilayered piezoelectric element of each of Examples 90 and 91, the ultrasonic motor illustrated in FIG. 6B was manufactured. It was confirmed that the motor rotated in accordance with an applied alternating voltage.
Example 109
Through the use of the ultrasonic motor of Example 108, the optical device illustrated in FIGS. 7A and 7B was manufactured. It was confirmed that the automatic focus operation was performed in accordance with an applied alternating voltage.
Example 110
Through the use of the multilayered piezoelectric element of each of Examples 90 and 91, the dust removing device illustrated in FIGS. 9A and 9B was manufactured. Plastic beads were scattered, and an alternating voltage was applied. Then, it was confirmed that satisfactory dust removing efficiency was exhibited.
Example 111
Through the use of the dust removing device of Example 110, the imaging device illustrated in FIG. 12 was manufactured. During operation, the dust on the surface of the imaging unit was satisfactorily removed, and an image without a dust defect was obtained.
Example 112
Through the use of the multilayered piezoelectric element of each of Examples 90 and 91, the electronic device illustrated in FIG. 14 was manufactured. It was confirmed that the speaker operated in accordance with an applied alternating voltage.
INDUSTRIAL APPLICABILITY
The piezoelectric material of the present invention expresses satisfactory piezoelectricity even at high ambient temperature. Further, the piezoelectric material of the present invention has a small load on the environment because it is free of lead. Accordingly, the piezoelectric material of the present invention can be used efficiently for devices using a great amount of piezoelectric material such as a liquid discharge head, an ultrasonic motor, and a dust removing device.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2012-186642, filed Aug. 27, 2012, which is hereby incorporated by reference herein in its entirety.
REFERENCE SIGNS LIST


    1 first electrode
    2 piezoelectric material
    3 second electrode
    101 piezoelectric element
    102 individual liquid chamber
    103 diaphragm
    104 liquid chamber partition wall
    105 discharge port
    106 communicating hole
    107 common liquid chamber
    108 buffer layer
    1011 first electrode
    1012 piezoelectric material
    1013 second electrode
    201 oscillator
    202 rotor
    203 output shaft
    204 oscillator
    205 rotor
    206 spring
    2011 elastic ring
    2012 piezoelectric element
    2013 organic adhesive
    2041 metal elastic body
    2042 multilayered piezoelectric element
    310 dust removing device
    320 diaphragm
    330 piezoelectric element
    331 piezoelectric material
    332 first electrode
    333 second electrode
    336 first electrode plane
    337 second electrode plane
    51 first electrode
    53 second electrode
    54 piezoelectric material layer
    55 internal electrode
    501 first electrode
    503 second electrode
    504 piezoelectric material layer
    505a internal electrode
    505b internal electrode
    506a external electrode
    506b external electrode
    601 camera main body
    602 mount portion
    605 mirror box
    606 main mirror
    200 shutter unit
    300 main body chassis
    400 imaging unit
    701 front unit lens
    702 rear unit lens (focus lens)
    711 attaching/detaching mount
    712 fixed barrel
    713 linear guide barrel
    714 front unit barrel
    715 cam ring
    716 rear unit barrel
    717 cam roller
    718 axial screw
    719 roller
    720 rotation transmission ring
    722 roller
    724 manual focus ring
    725 ultrasonic motor
    726 waved washer
    727 ball race
    728 focus key
    729 joining member
    732 washer
    733 low friction sheet
    881 liquid discharge device
    882 sheathing
    883 sheathing
    884 sheathing
    885 sheathing
    887 sheathing
    890 recovery unit
    891 recording unit
    892 carriage
    896 device main body
    897 automatic sheet feeder unit
    898 output port
    899 conveyance unit
    901 optical device
    908 release button
    909 stroboscopic light emission unit
    912 speaker
    914 microphone
    916 fill light unit
    931 main body
    932 zoom lever
    933 power button

## Claims

1. A piezoelectric material that is free of potassium, comprising a perovskite-type metal oxide represented by general formula (1):


(NaxM1-y)(Zrz(Nb1-wTaw)y(Ti1-vSnv)(1-y-z))O3  (1),

where M represents at least any one of Ba, Sr, and Ca, and relationships of 0.80≦x≦0.95, 0.85≦y≦0.95, 0<z≦0.03, 0≦v<0.2, 0≦w<0.2, and 0.05≦1-y-z≦0.15 are satisfied.

2. The piezoelectric material according to claim 1, wherein the piezoelectric material satisfies a relationship of w=0 in the general formula (1).

3. The piezoelectric material according to claim 1, wherein the piezoelectric material satisfies a relationship of v=0 in the general formula (1).

4. The piezoelectric material according to claim 1, wherein the perovskite-type metal oxide is represented by general formula (2):


(NaxBa1-y-a-bCaaSrb)(ZrzNbyTi1-y-z)O3  (2),

where relationships of 0.80≦x≦0.95, 0.85≦y≦0.95, 0<z≦0.03, 0.05≦1-y-z≦0.15, 0≦a≦0.1, 0≦b≦0.1, and 0≦a+b≦0.15 are satisfied.

5. The piezoelectric material according to claim 1, further comprising more than 0 mol % to 2 mol % or less of Cu with respect to 1 mol of the perovskite-type metal oxide.

6. The piezoelectric material according to claim 1, wherein the piezoelectric material satisfies a relationship of x<y in the general formula (1).

7. A piezoelectric element, comprising at least:
a first electrode;
a piezoelectric material; and
a second electrode,
wherein the piezoelectric material comprises the piezoelectric material according to claim 1.

8. A multilayered piezoelectric element, comprising a piezoelectric material layer and an electrode layer including an internal electrode, which are alternately stacked,
wherein the piezoelectric material comprises the piezoelectric material according to claim 1.

9. The multilayered piezoelectric element according to claim 8, wherein the internal electrode contains Ag and Pd, and a weight ratio M1/M2 of a content weight M1 of the Ag to a content weight M2 of the Pd satisfies a relationship of 1.5≦M1/M2≦9.0.

10. The multilayered piezoelectric element according to claim 8, wherein the internal electrode contains at least one kind of Ni and Cu.

11. A manufacturing method for the multilayered piezoelectric element as defined in claim 8, comprising at least:
a step (A) of obtaining a slurry by dispersing a metal compound containing Na, Nb, Ti, and Zr;
a step (B) of obtaining a compact from the slurry;
a step (C) of forming an electrode on the compact; and
a step (D) of obtaining a multilayered piezoelectric element by sintering a compact in which the compact containing the metal compound and the electrode are stacked alternately, the step (D) being performed at a sintering temperature of 1,200° C. or less.

12. A liquid discharge head, comprising at least:
a liquid chamber comprising a vibration unit including the piezoelectric element according to claim 7; and
a discharge port communicating to the liquid chamber.

13. A liquid discharge device, comprising:
a conveyance unit for a recording medium; and
the liquid discharge head according to claim 12.

14. An ultrasonic motor, comprising at least:
a vibration body including the piezoelectric element according to claim 7; and
a moving body to be brought into contact with the vibration body.

15. An optical device, comprising a drive unit including the ultrasonic motor according to claim 14.

16. A vibration device, comprising a vibration body including the piezoelectric element according to claim 7.

17. A dust removing device, comprising a vibration unit including the vibration device according to claim 16.

18. An imaging device, comprising at least:
the dust removing device according to claim 17; and
an imaging element unit,
wherein a vibration member of the dust removing device and a light receiving plane of the imaging element unit are sequentially disposed on the same axis.

19. An electronic device, comprising a piezoelectric acoustic component including the piezoelectric element according to claim 7.

20. A liquid discharge head, comprising at least:
a liquid chamber comprising a vibration unit including the multilayered piezoelectric element according to claim 8; and
a discharge port communicating to the liquid chamber.

21. A liquid discharge device, comprising:
a conveyance unit for a recording medium; and
the liquid discharge head according to claim 20.

22. An ultrasonic motor, comprising at least:
a vibration body including the multilayered piezoelectric element according to claim 8; and
a moving body to be brought into contact with the vibration body.

23. An optical device, comprising a drive unit including the ultrasonic motor according to claim 22.

24. A vibration device, comprising a vibration body including the multilayered piezoelectric element according to claim 8.

25. A dust removing device, comprising a vibration unit including the vibration device according to claim 24.

26. An imaging device, comprising at least:
the dust removing device according to claim 25; and
an imaging element unit,
wherein a vibration member of the dust removing device and a light receiving plane of the imaging element unit are sequentially disposed on the same axis.

27. An electronic device, comprising a piezoelectric acoustic component including the multilayered piezoelectric element according to claim 8.